This application claims Paris Convention Priority of German patent application number 197 46 510.2 filed Oct. 22, 1997 the complete disclosure of which is hereby incorporated by reference.
The invention concerns a device for passing through pipes in the form of a pig moved through the pipe and guided along the inner walls thereof with at least one pig body and with support elements disposed on its outer periphery for guiding in the pipe as well as drive elements in the form of collars for advancement within the pipe.
Pigs are used in pipelines, in particular for oil and gas transport, to locate defects in the pipe, for cleaning the pipe, and the like. They are thereby normally advanced through the pipe by the medium being transported e.g. oil. Intelligent pigs carry out the most differing of measurements, such as pipe wall measurements to e.g. detect local corrosion, wall thickness weaknesses caused by mechanical damage, pitting etc. Depending on the job at hand, differing types of sensor units are utilized, such as leakage sensors, Hall effect sensors, electro-optical sensors, ultrasound sensors or the like.
In order to be able to advance the pig within the pipe using the medium transported therein, the pig has a pig body comprising collars which seat tightly on the inner side of the pipe and are subjected to the flow pressure of the medium being transported.
In order to be able to check pipes which are under water or below the earth""s surface, each pig must be introduced into the pipes through an entrance location. In particular for the case of underwater conduits, this is extremely expensive, since complicated and expensive lock mechanisms having expensive valves must be provided therefor. To effect entrance, it is then necessary for a diver to dive to substantial depths in order to be able to introduce the pig into the pipe being examined. Since the pipes for the medium being transported, e.g. oil, are laid at up to 300 m of depth in water and since they have a substantial diameter of e.g. 42 inches, such an entrance lock mechanism having a diameter of this size cannot be passed from the bottom up to the surface of the water, since the weight of such a entrance pipe would be prohibitive.
For this reason, it is the underlying purpose of the invention to create a device of the above mentioned kind which facilitates a simple entrance into a pipe conduit while avoiding the above mentioned disadvantages.
This purpose is achieved in accordance with the invention with a device for inspection of pipes of the above mentioned kind in that at least one of the collars is configured in a radially expandable fashion. The radial expansion preferentially is effected by pivoting.
The solution in accordance with the invention allows the pigs to be introduced through entrance pipes having small diameters e.g. a diameter of 28 inches (corresponding to approximately 60 cm) and into a main conduit of 40 inches (corresponding to 1 m). The collars effecting the advancement have a smaller diameter in the entrance pipe which first expands into one of larger diameter upon entrance into the main pipe. In this manner, advancement of the inspecting pig can be reliably effected both in the entrance pipe as well as in the main pipe.
A preferred embodiment provides that the expandable collar has an expanded diameter which is larger than that of collars whose radius is constant. Whereas the former expandable collars serve for transport of the pig in the main conduit or pipe of 42 inches, the collars having a non-changing radius provide for transport in the entrance pipe having a diameter of 28 inches.
At least one of the collars having fixed radius is preferentially disposed as a nose on the front side of the pig facing the direction of motion. These so-called xe2x80x9cnose collarsxe2x80x9d serve for reliable drive of the pig in the entrance pipe and for removing the pig from the entrance pipe.
In a further improvement, the radially expandable collars are self-expanding. No auxiliary measures are thereby needed to erect the collars upon transition from the entrance pipe into the main pipe so that they assume their expanded position in the transitional region automatically and reliably. In order to achieve this, the radially expandable collars preferentially comprise a spider which can angle-off about the periphery thereof at least once opposite to the drive direction of the pig and having a plurality of radially extended braces as well as at least one sealing disc disposed on the braces and made from flexible material. The spider is preferentially made from polyurethane. The spider guarantees the folding-up of the collar in the entrance pipe of smaller diameter so that the collar is inactive during this time, while simultaneously effecting erection of the collar when passing from the entrance pipe into the main pipe. The spider furthermore keeps the collar stiff during passage of the pig through the pipe being inspected. The sealing disc reliably seals those regions of the spider which are left open by the radially extending braces so that the medium reliably interacts with the collar to drive the pig.
A further improvement prevents the expandable collar from flipping over during expansion in that the expandable collar is held in its expanded position by anchor elements which can seat on the pig body prior to expansion and are fixed thereto. These elements are preferentially flexible members such as chains. The anchor elements can also however be telescoping elements or could be rods in linked connection with another. A combination of these types of anchor elements is also possible.
In order that the expandable collars are pressed against the pipe to be inspected when they are loaded by the flow pressure, the collars preferentially have a substantially plate-like shape when expanded. The collar serving as the nose element is preferentially ring shell shaped.
In a further preferred embodiment, radially expandable support and guide rollers are provided (relative to the drive direction of the pig) behind each expandable collar. These support and guide rollers, in a further improvement, are fixed on arms which can be outwardly displaced to seat at the inner wall of the pipe under the action of a spring force. This type of support and guide rollers or roller sets formed by such support and guide rollers, guide the pig body along the inner wall of the pipe. The roller sets align the moving pig within the pipe and reduce wear on the outer periphery of the collar. Since these roller sets are also expandable in the radial direction, they can likewise seat on the pig body during introduction through the entrance pipe or can be slightly separated from the pig body to also provide for alignment of the pig in the entrance pipe during the entrance process.
A further preferred embodiment provides that the pig comprises two pull units linked to each other and having support and guide rollers of which only the (as seen in the drive direction) first pull unit has an expandable collar. The first unit thereby serves as the actual pull unit to guarantee the drive function during inspection in the main pipe. The second pull unit secures the drive during transition from the narrower entrance pipe into the larger main pipe. In order to guarantee sufficient stability for the individual pull units, each pull unit is thereby provided with at least two sets of support and guide rollers. In addition, at least one collar having a non-changing radius is provided for on each pull unit which is substantially disc-shaped. These collars guarantee drive in both pull units and thereby the transport of the entire pig. If the first pull unit is already located in the main pipe during the transition from the entrance pipe into the main pipe, wherein its collar is radially erected, the drive function is assured during this time by the second pull unit and the collar disposed thereon, still located in the entrance pipe. When the second pull unit enters into the main pipe, the collars as well as the support and guide rollers of the first pull unit have already been erected to guarantee continued motion in the main pipe. The flat configuration for the additional collar takes into consideration the limited space on the pull unit and in the entrance pipe.
After the pig has reached the main pipe, pig drive is effected by the first pull unit and the expandable collars disposed thereon along with the support and guide rollers and the second pull unit is no longer needed for stabilizing the first pull unit and for drive purposes. In accordance with an improvement, the second pull unit acting as a guide unit is therefore axially displaceable relative to the first unit. It can thereby move towards the pig inspection units and stabilize the pig.
Further advantages and features of the invention can be derived from the claims and the following description in which an embodiment is described in greater detail with reference to the drawing.